Acoustical wave filter



March 18, 1930. c, HAYES 1,751,035

ACOUSTICAL WAVE FILTER Filed March 5, 1927 I gvwenfoz wy/6 c. Ha es Patented Mar.'1s,f1 93o UNITED- ,STATES PATENT OFFICE ncousrrcar. WAVE rmrnn Application filed March 3,

1927. Serial m3. 172,391.

Gasman mm m or or macn s, 1888, as anannnn nan. so, 192a; 370 o. e. 751

My invention relates broadly to acoustical I wave filters in which standing wave systems within tubes are utilized and relates more particularly to the application of the same to radio receiving set The object of my invention 1s to eliminate static or stragys in a radio receiving system and to ampli the pure signal received from the transmission station free from all ex- 10 traneous noises. g

The energy. of a standing wave system within a tube has been found .to be wholly kinetic at the loops and wholly potential at the nodes.vv Little or 'no energy,'therefore, is expended against the tube at the loops of the signal since at this point the pressure outwardly from within the tube is equal to atmospheric pressure.

Applying this principleto radio receivers I have developedan acoustical wave filter that transmits waves of predetermined p length without appreciable loss whereas those waves having a wavelength at variance with the selected waves will expend their energyvand reduce their volume prior to detection or further amplification. r invention consists substantially in the construction, combination, and arrangement of parts'associatfed therewith or as will be more fully hereinafter set forth as shown. by the' accompanying drawings and finally ,pointed out in the appended claims.

-Reference is to be had to the accompanying drawing forming apart'of this specification in which like reference characters indicate corresponding parts throughout the several views and in which 1 Figural represents a radio receiving cir cuit in which such a device may be used, 40 and-- v Figure 2, represents a preferred construe tion of one form of my invention. V Figure 3 is an .end' View in section of one modification showing the 'arrangementof a plurality of tubes of structure similar to that shown in Figure 2.

Referring "to Figure 2, numeral 1 represents the input terminals of a sound generating device 2, to which the output terminals 1' of Figure l are connected. The sound generating device, such as a telephone 'receiver, consists of a sound generating diaphragm 7 actuated by the electrical current output of the radio receiver thus generating a sound having a frequency equal to that of the driving current. a I The output from the sound generator traverses the .tube 3, that has.a rigid inert wall and which for simplicity of illustration and description is terminated by a sound reproducer 4 similar to the one 2 at the input end of the tube and which has been briefly-described. However, I do not wish to limit myself to the use of input and output devices-of similar structure.

Sound waves generated by diaphragm 2 traversing tube, 3 cause the diaphragm 5 of the .terminal -magnetophone 4 to vibrate thereby generating an alternating electro-- motive force at its terminals 6 of the same 10 frequency as that of the generating sound waves. This electromotive force can be used. directly or in amplified form to energize an ordinary telephone or loud speaker. 1 If the frequency of the current driving 7 diaphragm 7 is made of proper value, a standing wave system as represented at 8 will be formed in the tube 3 between the two diav phragms 7, and 5. In practice the tube 4 length is made such that thestanding wave system will be formed for a sound pitched at a frequency approximately IOOO-Vibrations per second. f

This value is chosen for the reason that the ear is highly sensitive to sounds of this frea5 I quency and because most radio operators 1 prefer to receive signals of this pitch.

The tpbe is made up of a. plurality of sections 9, each "section of which is separated from each other by slots 10. The length of i I each section9 of the'tube 3 is such that these slots 10 are located at the loops of the standinfgwave system.8 in the tube 3. The energy of such a standing wave system being' wholly potential at the nodes and wholly kinetic at the loops it follows, therefore, that little or no ener will escape from the .tube if it is punctur or slotted transverselfit the loops since the pressure against the tu wall at those points is equal to the atmospheric pressure upon the outside of the tube. It is evident that the distance between slots along the tube is equal to'a half wavelength of the sound that is transmitted substantially'without loss. i

Sounds of any other wavelength will not 7 pass the'slots or perforations 10 without loss -of energy through the slots to the outside because the energy of the waves at those points will not then be wholly kinetic.

v In articular the sounds generated by the socal ed static components of the current are largely of the nature of impulses of a wide ran e of wave lengths. Since only a very sma 1 percentage of the impulses produced thereby will coincide with the standing wave system 8 practically all of the impulses will be lost through the slots 10 and onl the pure signal will be left when the stan ing wave system reaches the diaphragm 5 of the output'magnetophone 4:.

other than the predeterminedcomponent of said standing wave and means for reconverting the undissipated acoustic energy iilto nonacoustic energy.

2. An acoustic filter'comprisin'gmeans for converting non-acoustic energy into acoustlc energy, said acoustic energy beingin the form of a standing wave having aplurality of com-v ponents, means resonant to a predetermined component of said standing wave,a plurality of energy dissipating means in fixed positional relation to said resonant means and lo- I cated at-points on said resonant means where the energy of'said predetermined component is wholly in kinetic form and means for reconverting the undissipated acoustic energy into non-acoustic energy; -V

' -HARVEY C. HAYES.

As a result, the magnetophone 4 responds less rigorously to the static impulses thanto the pure tone signal since the pure tone traverses the tube in volume.

The effectiveness of the device is dependent to a large extent on the number of sections of the tube and'also on its diameter. In practice a tube one half an inch inside diameter and consisting of 10 sections has given good resu ,ts. v

A modification still'more eflicient is the practically "undiminished identical with those. described in the operations of the device as Figure 1.

- It will be understood that the'above descriptlon and accompanying drawings comprehend'only the general andreferred emin tail changes construction, and arrangebodiment of my invention and t at minor dement of parts 'may be made within the sec e of the ap I nded claims and without sacri cmg any 0 the advantages of my invention. so

The invention herein described may be manufactured and used by or for the Government of the United States forgovernmental Q purposes without thep'afyment to meof any royi lty thereonor there or.

utilization of aplurality of tubes of smaller aving thus myinvention what Y I claim is- 1. An-acousticfiIter comprising means for convertin' non-acoustic ener into acoustic energy said acoustic energy being inv the form.

.of a standing wave having a plurality offcomp'onents',-means resonant a predetermined component of said standing wave, a'p'lurality of energy dissipating in fixed positional relation said resonantmeans and so positioned as only to dissipate energy from 

